GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Power Brake Booster

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The power brake booster is a tandem vacuum suspended unit. Some models may be equipped with a single or dual function vacuum switch which activates a brake warning light should low booster vacuum be present. Under normal operation, vacuum is present on both sides of the diaphragms. When the brakes are applied, atmospheric air is admitted to one side of the diaphragms to provide power assistance.

REMOVAL & INSTALLATION



1994-97 Models

See Figures 1 and 2

  1. Apply the parking brake and block the drive wheels.
  2.  
  3. Remove the master cylinder-to-power brake booster nuts, then reposition the master cylinder and combination valve out of the way; if necessary, support the master cylinder on a wire to prevent damaging the brake lines.
  4.  

When removing the master cylinder from the power brake booster, it is not necessary to disconnect the hydraulic lines, therefore the brake system should not have to be bled.

  1. Disconnect the vacuum hose from the power brake booster.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: Common power brake booster attachment

  1. From under the dash, remove the retainer and washer from the brake pedal on 1994 utility models. On all other models, remove the retainer and brake switch from the brake pedal.
  2.  
  3. Disconnect the pushrod from the brake pedal.
  4.  
  5. From under the dash, remove the power brake booster-to-cowl retaining nuts.
  6.  
  7. Back under the hood, remove the power brake booster and the gasket from the cowl.
  8.  

To install:
  1. Position the booster to the cowl using a new gasket.
  2.  
  3. Install the booster retaining nuts and tighten to 16 ft. lbs. (22 Nm) 1994 utility models, 24 ft. lbs. (32 Nm) on 1994 pick-up models and 27 ft. lbs. (36 Nm) on all 1995-97 models.
  4.  
  5. Connect the pedal pushrod and install the washer or switch and the retainer.
  6.  
  7. Connect the vacuum hose.
  8.  



Click image to see an enlarged view

Fig. Fig. 2: Checking the piston booster rod using the gauge tool

  1. For all vehicles covered in this guide, gauge the booster rod:
    1. Apply 25 in. Hg (85 kPa) of vacuum using a hand held vacuum pump or apply maximum engine vacuum.
    2.  
    3. Check the maximum and minimum rod lengths using J-37839 or an equivalent pushrod height gauge.
    4.  
    5. If the piston is not within limits, install a service adjustable piston rod and adjust it to the correct length.
    6.  

  2.  
  3. Reposition the master cylinder and combination valve bracket to the booster studs, then secure using the retaining nuts. For details, please refer to the master cylinder procedure located earlier in this section.
  4.  
  5. Start and run the engine, then check for proper booster operation.
  6.  

1998-99 Models

See Figure 2

  1. Apply the parking brake and block the drive wheels.
  2.  
  3. Remove the master cylinder-to-power brake booster nuts, then reposition the master cylinder and combination valve out of the way; if necessary, support the master cylinder on a wire to prevent damaging the brake lines.
  4.  

When removing the master cylinder from the power brake booster, it is not necessary to disconnect the hydraulic lines, therefore the brake system should not have to be bled.

  1. Disconnect the vacuum hose from the power brake booster.
  2.  
  3. From under the dash, remove the retainer and brake switch from the brake pedal.
  4.  
  5. Remove the magnesium beam as follows:
    1. Remove the instrument panel as outlined in Suspension & Steering of this repair guide.
    2.  
    3. Disconnect the pushrod from the brake pedal.
    4.  
    5. Unfasten the four large flange nuts and the two bolts retaining the magnesium beam.
    6.  
    7. Unfasten the brake pedal bolts, remove the bushings and the spacer, and then separate the pedal from the magnesium beam.
    8.  

  6.  
  7. From under the dash, remove the power brake booster-to-cowl retaining nuts.
  8.  
  9. Back under the hood, remove the power brake booster and the gasket from the cowl.
  10.  

To install:
  1. Position the booster to the cowl using a new gasket.
  2.  
  3. Install the booster retaining nuts and tighten to 30 ft. lbs. (40 Nm).
  4.  
  5. Install the magnesium beam as follows:
    1. Install the brake pedal bushings into the brake pedal and position the pedal onto the beam. Install the pedal retainer and tighten to 19 ft. lbs. (25 Nm).
    2.  
    3. Place the beam into position and tighten the nuts and bolts to 18 ft. lbs. (25 Nm).
    4.  

  6.  
  7. Connect the pedal pushrod and install the switch and the retainer.
  8.  
  9. Connect the vacuum hose.
  10.  
  11. For all vehicles covered in this guide, gauge the booster rod:
    1. Apply 25 in. Hg (85 kPa) of vacuum using a hand held vacuum pump or apply maximum engine vacuum.
    2.  
    3. Check the maximum and minimum rod lengths using J-37839 or an equivalent pushrod height gauge.
    4.  
    5. If the piston is not within limits, install a service adjustable piston rod and adjust it to the correct length.
    6.  

  12.  
  13. Reposition the master cylinder and combination valve bracket to the booster studs, then secure using the retaining nuts. For details, please refer to the master cylinder procedure located earlier in this section.
  14.  
  15. Start and run the engine, then check for proper booster operation.
  16.  

 
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